1. Field of the Invention
The invention relates to a liquid crystal display device comprising an input panel for detecting input information, made up of a pair of transparent substrates with an electrode provided on respective inner surfaces thereof, facing each other, and disposed on the visible side of a liquid crystal display panel made up by filling a gap between a pair of substrates with liquid crystal, and in particular, to a reflective or transflective liquid crystal display device.
2. Description of the Related Art
Many matrix type liquid crystal display panels have recently been put to use for a display of various information terminals, instruments, personal computers, and so forth. In particular, for portable information equipment, there have been in widespread use reflective liquid crystal display devices capable of effecting display by making use of ambient light in order to realize lower power consumption or transflective liquid crystal display devices capable of effecting reflective display when the surroundings are bright and effecting transmissive display by lighting up an auxiliary light source incorporated therein when the surroundings are dark.
With the portable information equipment, while reduction in weight and thickness is important from the viewpoint of portability, use of a liquid crystal display panel having a large area is preferable from the viewpoint of visibility. For this reason, it has been in practice to reconcile miniaturization of a liquid crystal display device with enlargement of a display area thereof by installing an input panel as an input device on a display surface (display region) of the liquid crystal display panel such that display can be recognized through the input panel.
As the input panel for use in this case, there is available, for example, a touch panel of a resistive membrane type, made up of an upper substrate and a lower substrate, both transparent, with an upper electrode and a lower electrode provided on the inner surfaces of the respective substrates, facing each other, in such a way as to be deformable by applying pressure to either the upper substrate or the lower substrate (mainly the upper substrate), so that the upper substrate is caused to come into contact with the lower substrate as a result of such deformation, thereby enabling position coordinates of pressed parts of the upper substrate or the lower substrate to be read.
Although the touch panel of this type has been in widespread use because it is convenient to use, and has excellent recognizability while its fabrication cost is low, it has had a problem of causing deterioration in visibility of the liquid crystal display panel when it is disposed so as to overlay the display region of the liquid crystal display panel.
Cited as the reasons for such a problem are occurrence of absorption of light by respective light transmitting members, reflection due to the difference in refractive index between the light transmitting members in contact with each other, and occurrence of coloring caused by absorption or interference because the disposition of the touch panel on the visible side (the viewer""s side) of the liquid crystal display panel will have the same effect as that in the case where a plurality of light transmitting members are disposed on the visible side of the liquid crystal display panel. Accordingly, there will arise problems that, as compared with the case of employing the liquid crystal display panel alone, display becomes darker, a contrast ratio deteriorates, coloring occurs, and a quantity of incident light decreases due to reflection of light by the touch panel.
Among the methods of solving these problems, there are available a method of reducing reflection by inserting an optical member, capable of reducing the difference in refractive index, between respective constituent members, a method of reducing a quantity of absorbed light by reducing the thickness of the respective constituent members, or a method of selecting constituent members having a low absorption ratio for use, and a method of reducing the number of the constituent members.
Further, there is another method of preventing reflection of light by the touch panel by disposing a polarizer on the visible side of the touch panel, and disposing a quarter-wave (lambda: xcex) plate on the rear face side of the polarizer, however, in this case, there is the need for disposing one more sheet of polarizer between the liquid crystal display panel and the touch panel, and consequently, it follows that light is transmitted through two sheets of the polarizers twice when effecting reflective display, so that there will be an increase in absorption of light, resulting in darker display.
Besides the above, as a construction for preventing reflection of light, there is available a construction wherein a filling medium having a refractive index, equivalent to the mean between the refractive index of the upper electrode as well as the lower electrode, made up of a transparent and electrically conductive film, and the refractive index of air, is sealed between the upper substrate and the lower substrate of the touch panel, however, even with such a construction as described, reflection occurs between the lower substrate of the touch panel and a first substrate of the liquid crystal display panel, so that reduction in reflection of light has been found insufficient.
Further, particularly, in the case of a liquid crystal display panel using supertwisted nematic (STN) liquid crystal, and a reflective or transflective liquid crystal display panel having three-terminal thin film transistors (TFTs) or two-terminal thin film diodes (TFDs), and using twisted nematic (TN) liquid crystal or parallel alignment liquid crystal, there is the need for a reflector or a transflective reflector, and a polarizer as well as a retardation film on the viewer""s side of the former. With the use of these constituent members, bright display and dark display are effected.
Accordingly, if a constituent member for preventing reflection of light from the touch panel is additionally laminated on top of such a liquid crystal display panel as described above, this will create problems such as an increase in the number of the constituent members thereof, an increase in quantity of light absorbed, and an increase in the weight as well as thickness of the liquid crystal display device, resulting in an increase in the cost of the device. Thus, improvement in these respects has been highly desired.
Furthermore, although there is another method of employing a film substrate for the upper substrate or lower substrate of the input panel, this has caused a problem that the display contents of the liquid crystal display panel is distorted or unevenness in reflective intensity is increased due to swelling (distortion) of the film substrate.
In order to solve the problem described, it is conceivable to adopt a constitution wherein the first substrate of the liquid crystal display panel doubles as the lower substrate of the input panel. In this case, however, during the process of fabricating a first electrode to be installed on the side of the first substrate of the liquid crystal display panel, facing a liquid crystal layer, or during the process of fabricating the liquid crystal display panel, there is involved the risk that a change occurs to a resistance value of the transparent and electrically conductive film of the input panel, depending on a temperature at which the process as described is carried out, and deterioration in unevenness or damage occurs to the transparent and electrically conductive film, so that the constitution described is not suitable for fabrication of a high quality liquid crystal display device.
In order to solve various problems described in the foregoing, it is an object of the invention to prevent deterioration of visibility of the liquid crystal display panel due to the effect of the input panel, and to realize reduction in the number of constituent members absorbing light, reduction in weight, a lower profile, reduction in cost, prevention of distortion of images in display, and enhancement in contrast, in a liquid crystal display device wherein an input panel such as a touch panel is disposed on the visible side of a liquid crystal display panel so as to overlay the latter, and display effected by the liquid crystal display panel is watched through the input panel.
To this end, a liquid crystal display device according to the invention comprises a liquid crystal display panel made up by coupling a first substrate and a second substrate having an electrode provided on respective inner surfaces thereof facing each other, with a predetermined gap provided therebetween, and by filling the gap with a liquid crystal layer, and an input panel made up by coupling an upper substrate and a lower substrate, both of which are transparent, having an electrode provided on respective inner surfaces thereof facing each other, with a predetermined gap provided therebetween, the first substrate on the visible side of the liquid crystal display panel being disposed so as to be opposed to the lower substrate of the input panel, wherein a double-sided adhesive layer having a surface area equivalent to that of a display region of the liquid crystal display panel is disposed between the first substrate and the lower substrate.
The gap between the upper substrate and the lower substrate of the input panel is preferably filled with a filling medium. The double-sided adhesive layer described above has preferably optical diffusibility. Further, the double-sided adhesive layer more elastic than spacers or a sealing member for maintaining the gap of the liquid crystal display panel is preferably used.
Otherwise, in place of the double-sided adhesive layer, a mutual filling medium (either the same medium as a filling medium filling the input panel or a medium different therefrom) may be provided between the first substrate of the liquid crystal display panel and the lower substrate of the input panel by sealing the same therein-between with a mutually sealing member.
With the liquid crystal display device having those features as described above, a reflector or a transflective reflector is preferably disposed on the face of the second substrate of the liquid crystal display panel, on the side of the liquid crystal layer, and at least one sheet of retardation film and one sheet of polarizer are preferably disposed in that order from the side of the upper substrate on the visible side of the upper substrate of the input panel. Further, the retardation films preferably include at least one sheet of twisted retardation film.
Or, an auxiliary light source is preferably disposed on the side of the second substrate, opposite from the side of the liquid crystal layer with a polarizer interposed therebetween.
Furthermore, switching elements may be disposed on the first substrate or the second substrate of the liquid crystal display panel so that display is effected by the liquid crystal display panel applying electric signals to the liquid crystal layer via the switching elements.
The upper substrate as well as the lower substrate of the input panel may be a retardation film.
Further, with the liquid crystal display device according to the invention, no filling medium may fill a gap between the upper substrate and the lower substrate of the input panel, and a second retardation film, a first retardation film, and a first polarizer may be disposed in that order by laminating one on top of the other from the side of the upper substrate of the input panel on the viewer""s side of the upper substrate.
With the liquid crystal display device, the upper substrate and the lower substrate of the input panel are preferably substrates having a substantially even retardation value within the plane thereof or optically isotropic substrates having a retardation value nearly at zero, respectively.
Further, the first retardation film is preferably a half-wave film and the second retardation film is preferably a quarter-wave film.
With the liquid crystal display device, a transflective reflector is preferably disposed on the face of the second substrate of the liquid crystal display panel, on the side of the liquid crystal layer, and at least one sheet of retardation film, a second polarizer, and an auxiliary light source are preferably disposed on the side of the second substrate, opposite from the side of the liquid crystal layer, in that order from the side of the second substrate.
On the first substrate or the second substrate described above, switching elements may be disposed so that display is effected by the liquid crystal display panel described above by applying electric signals to the liquid crystal layer via the switching elements.
The input panel is preferably provided with positioning marks for aligning the absorption axis of the polarizer disposed on the touch panel with the alignment directions of liquid crystal molecules of the liquid crystal layer filling the gap of the liquid crystal display panel.
The upper substrate, the first retardation film, the second retardation film, and the first polarizer are preferably bonded to each other with an adhesive.
The external shape of the first polarizer is equivalent in size to or smaller than that of the first retardation film, the second retardation film, and the upper substrate, respectively.
With the respective liquid crystal display devices, it is preferable that a liquid crystal display panel connection portion for connecting the liquid crystal display panel to a driving circuit for the liquid crystal display panel is disposed in a peripheral region of the first substrate of the liquid crystal display panel, on one side thereof, while an input panel connection portion for connecting the input panel to a driving circuit for the input panel is disposed in a peripheral region of the lower substrate of the input panel, on one side thereof, the one side of the first substrate where the liquid crystal display panel connection portion is disposed is on the same side as the one side of the lower substrate where the input panel connection portion is disposed, and input panel connection means for connecting the input panel connection portion and the driving circuit for the input panel are installed along the side face of the lower substrate and the first substrate.
The input panel described above is preferably provided with at least four units of electrodes for detection of position, comprising at least a pair of X-electrodes and at least a pair of Y-electrodes, and wiring electrodes for providing wiring between each of the electrodes for detection of position and the input panel connection portion, and at least three lengths of the wiring electrodes are preferably disposed in a region where the same horizontally overlays the liquid crystal display panel connection portion as seen from the visible side.
Further, a first adhesive layer, a polarizer, a second adhesive layer, and a protective film are preferably disposed in that order from the side of the upper substrate of the input panel by laminating one on top of the other on the visible side of the upper substrate.
A first adhesive layer, at least one layer of retardation layer, a second adhesive layer, a polarizing layer, a third adhesive layer and a protective film may be disposed in that order from the side of the upper substrate by laminating one on top of the other on the visible side of the upper substrate.
The above and other objects, features and advantages of the invention will be apparent from the following detailed description which is to be read in conjunction with the accompanying drawings.